In semiconductor processing, transistors may be formed on semiconductor wafers. The transistors may include a gate structure having a gate dielectric and a gate electrode, a source, a drain, and a channel region between the source and the drain. In CMOS (complimentary metal oxide semiconductor) technology, transistors may typically be of two types: NMOS (negative channel metal oxide semiconductor) or PMOS (positive channel metal oxide semiconductor) transistors. The transistors and other devices may be interconnected to form integrated circuits (ICs) which perform numerous useful functions.
The performance of the ICs may directly depend on the performance of the transistors. Transistor performance may be improved by providing a strain in the channel region. Specifically, NMOS transistor performance may be improved by providing a tensile strain in the channel region and PMOS transistor performance may be improved by providing a compressive strain in the channel region.